Electrochemical gas sensors are generally known. They usually have a plurality of electrodes, which are in conductive contact with an electrolyte liquid and form in this manner a galvanic cell, hereinafter also called electrochemical measuring cell. Both the composition of the electrolyte liquid and the material of which the electrodes consist are relevant for the specific detection of different analytes. A basic requirement is that the electrodes consist at least partly of a conductive material. In addition to different metals, carbon is therefore also a material of which the electrodes may be manufactured.
The use of diamond-like carbon (DLC) as a measuring electrode material in a gas sensor for toxic gases, for example, F2 or Cl2, is known in this connection from DE 199 39 011 C1. A measuring range to an order of magnitude of about 2 ppm can be covered with such an electrode.
DE 10 2006 014 713 B3 also discloses an electrochemical gas sensor with a carbon-based measuring electrode, namely, with a measuring electrode that contains carbon nanotubes. This can be used, for example, to detect analytes such as SO2 or diborane. However, there also is a relatively high cross sensitivity to other gases, e.g., H2 S or ozone.
Another prior-art carbon modification is graphene. Even though various different methods are known for manufacturing conductive graphene, e.g., by reducing graphene oxide by means of a camera flash (camera flash method) or by irradiation with UV light, it has not yet been possible to use graphene for manufacturing electrodes that can effectively be used in an electrochemical gas sensor. Even though it is possible by means of a camera flash method to prepare a layer that is conductive on its inside, the surface of the graphene oxide layer is destroyed in the process, so that no reaction is possible with the analytes reaching the layer from the outside. If a method that is gentle for the surface, e.g., irradiation with UV light is used, instead, there is a risk that the reaction will stop after the surface has been converted into graphene and the material located on the inside is not reduced. As a consequence, it is not possible to attain a sufficient conductivity to enable the electrode to be used effectively and in a sufficiently broad measuring range in an electrochemical gas sensor.